Polymer thin films has attracted much attention as a basic material for fabricating nanometric structures of organic assemblies. This research project has been performed in order to reveal fundamental properties of two-dimensional polymer systems such as polymer monolayer and ultra-thin polymer films from a view of polymer science. The issues focused in this project were listed as follows.1) Chain expansion of a single polymer in two-dimensional monolayer systems By using the energy transfer method, the root square mean distance of a single polymer chain was successfully evaluated in a monolayer system. From the comparison of the experimental value of energy transfer efficiency and the simulated value for two-dimensional chains, it was revealed that the polymer chains took contracted forms in the monolayer in order to minimize free area without chain entanglement at the surface.2) Chain conformation and entanglement in two-dimensional systems Molecular weight dependence of the shear viscosity for the air/water interfacial monolayers was investigated to elucidate chain morphology in the two-dimensional plane. The viscosity was proportional to the unit power of the molecular weight, indicating that there exists little entanglement of the polymer chains and each chain is segregated in the two-dimensional system.3) Structural relaxation mechanism and dynamics in monolayersThe microscopic motion of polymer chain in a monolayer was examined by time-resolved fluorescence depolarization method, and the rotational relaxation times were evaluated in a nanosecond scale. The dynamic behavior of polymer segment in the monolayer was revealed for the first time and indicated that the mobility is predominantly governed by the cohesive force of hydrophobic chains.